AddinferenceerrormessagesinWITnotebookmode

• Motivation for features / changes

If a model fails to run inference in WitWidget, no error is currently displayed so the user has no idea why WIT isn't working correctly. This change adds in proper error handling.

• Technical description of changes

Updated jupyter and colab witwidget code so that if inference throws any python error, it is properly caught and sent to the frontend.
The frontend now displays that inference error in a toast and in the status message.
Also fixed a small bug where when comparing 2 regression models, the initial Facets Dive view doesn't compare the two models.

• Screenshots of UI changes

• Detailed steps to verify changes work correctly (as executed by you)

Ran colab and jupyter notebooks with and without inference errors to see that the error message in both cases gets to the user.
Ran a two-model regression notebook to see proper default Dive display.

该提问来源于开源项目：tensorflow/tensorboard